约束
完整性约束
1.约束
- 约束条件与数据类型的宽度一样，都是可选参数
- 保证数据的完整性与一致性
- primary key(PK) 标识该字段为该表的主键，可以唯一的标识记录，每张表只有一个主键
- foreign key(FK) 标识该字段为该表的外键
- not null 标识该字段不能为空
- unique key(UK) 标识该字段的值是唯一的
- auto_increment 标识该字段的值自动增长（整数类型，而且为主键）
- default 为该字段设置默认值
- unsigned 无符号
- zerofill 使用0填充
2.说明
- 是否允许为空，默认null,可设置成not null,字段不允许为空，必须赋值
- 字段是否有默认值，缺省的默认值是null,如果插入记录时不给字段赋值，此字段使用默认值
- 是否是key
主键 primary key
外键foreign key
索引（index,unique...）
3.not null 与default
create table tb1(id int not null default 2,name char(5) not null);
表示id字段不能传空，传空默认值为2；name字段不能传空。
=========================not null======================= mysql> create table t1(id int); #id字段默认可以插入空 Query OK, 0 rows affected (2.02 sec) mysql> desc t1; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | +-------+---------+------+-----+---------+-------+ 1 row in set (0.04 sec) mysql> insert into t1 values(); #可以插入空 Query OK, 1 row affected (1.21 sec) mysql> select * from t1; +------+ | id | +------+ | NULL | #结果为null +------+ 1 row in set (0.00 sec) mysql> create table t2(id int not null); #设置id字段不为空 Query OK, 0 rows affected (2.04 sec) mysql> insert into t2 values(); #可以插入空 Query OK, 1 row affected, 1 warning (0.75 sec) mysql> desc t2; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | id | int(11) | NO | | NULL | | +-------+---------+------+-----+---------+-------+ 1 row in set (0.04 sec) mysql> select * from t2; +----+ | id | +----+ | 0 | #结果为0 +----+ 1 row in set (0.00 sec) ==================default==================== #设置id字段有默认值后，则无论id字段是null还是not null，都可以插入空，插入空默认填入default指定的默认值 mysql> create table t3(id int default 1); #设置默认值 Query OK, 0 rows affected (2.03 sec) mysql> insert into t3 values(); #可传空 Query OK, 1 row affected (0.79 sec) mysql> desc t3; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | id | int(11) | YES | | 1 | | +-------+---------+------+-----+---------+-------+ 1 row in set (0.04 sec) mysql> select * from t3; +------+ | id | +------+ | 1 | #结果为设置的默认值 +------+ 1 row in set (0.00 sec) mysql> alter table t3 modify id int not null default 1; #设置为不能传空 Query OK, 1 row affected (2.38 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql> desc t3; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | id | int(11) | NO | | 1 | | +-------+---------+------+-----+---------+-------+ 1 row in set (0.05 sec) mysql> select * from t3; +----+ | id | +----+ | 1 | #传空之后结果为默认值1 +----+ 1 row in set (0.00 sec) 练习： mysql> create table student1( -> name varchar(20) not null, -> age int(3) unsigned not null default 18, -> sex enum('male','female') default 'male', -> hobby set('play','study','read','music') default 'play,music' -> ); Query OK, 0 rows affected (2.04 sec) mysql> desc student1; +-------+------------------------------------+------+-----+------------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+------------------------------------+------+-----+------------+-------+ | name | varchar(20) | NO | | NULL | | | age | int(3) unsigned | NO | | 18 | | | sex | enum('male','female') | YES | | male | | | hobby | set('play','study','read','music') | YES | | play,music | | +-------+------------------------------------+------+-----+------------+-------+ 4 rows in set (0.04 sec) mysql> insert into student1(name) values('egon'); Query OK, 1 row affected (1.33 sec) mysql> select * from student1; +------+-----+------+------------+ | name | age | sex | hobby | +------+-----+------+------------+ | egon | 18 | male | play,music | +------+-----+------+------------+ 1 row in set (0.00 sec)
4.unique
- 设置唯一约束
方法一： mysql> create table department1( -> id int, -> name varchar(20) unique, -> comment varchar(100) -> ); Query OK, 0 rows affected (1.95 sec) mysql> desc department1; +---------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | varchar(20)| YES| UNI | NULL | | | comment | varchar(100) | YES || NULL | | +---------+--------------+------+-----+---------+-------+ 3 rows in set (0.04 sec) 方法二： mysql> create table department2( -> id int, -> name varchar(20), -> comment varchar(100), -> constraint uk_name unique(name) -> ); Query OK, 0 rows affected (2.05 sec) mysql> desc department2; +---------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name| varchar(20) | YES | UNI | NULL | | | comment | varchar(100) | YES | | NULL | | +---------+--------------+------+-----+---------+-------+ 3 rows in set (0.04 sec) mysql> insert into department1 values(1,'IT','技术'); Query OK, 1 row affected (1.84 sec) mysql> insert into department1 values(1,'IT','技术'); ERROR 1062 (23000): Duplicate entry 'IT' for key 'name'
- not null+unique:和primary key在某一字段表示不为空且唯一，但primary key只有一个，not null unique可以有多个
mysql> create table t10(id int not null unique); Query OK, 0 rows affected (0.34 sec) mysql> desc t10; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | id | int(11) | NO | PRI | NULL | | +-------+---------+------+-----+---------+-------+ 1 row in set (0.04 sec)
- 联合唯一
mysql> create table service( -> id int primary key auto_increment, -> name varchar(20), -> host varchar(15) not null, -> port int not null, -> unique(host,port) #联合唯一 -> ); Query OK, 0 rows affected (2.05 sec) mysql> insert into service values -> (1,'nginx','192.168.0.10',80), -> (2,'haproxy','192.168.0.20',80), -> (3,'mysql','192.168.0.30',3306); Query OK, 3 rows affected (1.83 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> insert into service(name,host,port)values('nginx','192.168.0.10',80); ERROR 1062 (23000): Duplicate entry '192.168.0.10-80' for key 'host' mysql>
5.primary key
- primary key字段的值不为空且唯一
- 一个表中可以单列做主键和多列做主键（复合主键）
- 一个表中只能有一个主键primary key
方法一：not null unique mysql> create table t10(id int not null unique); #主键 Query OK, 0 rows affected (0.34 sec) mysql> desc t10; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | id | int(11) | NO | PRI | NULL | | +-------+---------+------+-----+---------+-------+ 1 row in set (0.04 sec) 方法二：在某一字段后用primary key mysql> create table t11( -> id int primary key, #主键 -> name varchar(20), -> comment varchar(100)); Query OK, 0 rows affected (2.00 sec) mysql> desc t11; +---------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+-------+ | id | int(11) | NO | PRI | NULL | | | name | varchar(20) | YES | | NULL | | | comment | varchar(100) | YES | | NULL | | +---------+--------------+------+-----+---------+-------+ 3 rows in set (0.04 sec) 方法三：在所有字段后单独定义primary key mysql> create table department3( -> id int, -> name varchar(20), -> comment varchar(100), -> primary key(id)); Query OK, 0 rows affected (1.46 sec) mysql> desc department3; +---------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+-------+ | id | int(11) | NO | PRI | 0 | | | name | varchar(20) | YES | | NULL | | | comment | varchar(100) | YES | | NULL | | +---------+--------------+------+-----+---------+-------+ 3 rows in set (0.04 sec)
mysql> create table service1( -> ip varchar(15), -> port char(5), -> service_name varchar(10) not null, -> primary key(ip,port) -> ); Query OK, 0 rows affected (2.00 sec) mysql> desc service1; +--------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------------+-------------+------+-----+---------+-------+ | ip | varchar(15) | NO | PRI | | | | port | char(5) | NO | PRI | | | | service_name | varchar(10) | NO | | NULL | | +--------------+-------------+------+-----+---------+-------+ 3 rows in set (0.05 sec) mysql> insert into service values -> ('172.16.45.10','3306','mysqld'), -> ('172.16.45.11','3306','mariadb'); ERROR 1136 (21S01): Column count doesn't match value count at row 1 mysql> insert into service1 values -> ('172.16.45.10','3306','mysqld'), -> ('172.16.45.11','3306','mariadb'); Query OK, 2 rows affected (1.82 sec) Records: 2 Duplicates: 0 Warnings: 0 mysql> insert into service1 values ('172.16.45.10','3306','nginx'); ERROR 1062 (23000): Duplicate entry '172.16.45.10-3306' for key 'PRIMARY'
6.auto_increment
- 约束字段为自动增长，被约束的字段必须同时被key约束
#不指定id，则自动增长 create table student( id int primary key auto_increment, name varchar(20), sex enum('male','female') default 'male' ); mysql> desc student; +-------+-----------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+-----------------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(20) | YES | | NULL | | | sex | enum('male','female') | YES | | male | | +-------+-----------------------+------+-----+---------+----------------+ mysql> insert into student(name) values -> ('egon'), -> ('alex') -> ; mysql> select * from student; +----+------+------+ | id | name | sex | +----+------+------+ | 1 | egon | male | | 2 | alex | male | +----+------+------+ #也可以指定id mysql> insert into student values(4,'asb','female'); Query OK, 1 row affected (0.00 sec) mysql> insert into student values(7,'wsb','female'); Query OK, 1 row affected (0.00 sec) mysql> select * from student; +----+------+--------+ | id | name | sex | +----+------+--------+ | 1 | egon | male | | 2 | alex | male | | 4 | asb | female | | 7 | wsb | female | +----+------+--------+ #对于自增的字段，在用delete删除后，再插入值，该字段仍按照删除前的位置继续增长 mysql> delete from student; Query OK, 4 rows affected (0.00 sec) mysql> select * from student; Empty set (0.00 sec) mysql> insert into student(name) values('ysb'); mysql> select * from student; +----+------+------+ | id | name | sex | +----+------+------+ | 8 | ysb | male | +----+------+------+ #应该用truncate清空表，比起delete一条一条地删除记录，truncate是直接清空表，在删除大表时用它 mysql> truncate student; Query OK, 0 rows affected (0.01 sec) mysql> insert into student(name) values('egon'); Query OK, 1 row affected (0.01 sec) mysql> select * from student; +----+------+------+ | id | name | sex | +----+------+------+ | 1 | egon | male | +----+------+------+ row in set (0.00 sec)
#在创建完表后，修改自增字段的起始值 mysql> create table student( -> id int primary key auto_increment, -> name varchar(20), -> sex enum('male','female') default 'male' -> ); mysql> alter table student auto_increment=3; mysql> show create table student; ....... ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 mysql> insert into student(name) values('egon'); Query OK, 1 row affected (0.01 sec) mysql> select * from student; +----+------+------+ | id | name | sex | +----+------+------+ | 3 | egon | male | +----+------+------+ row in set (0.00 sec) mysql> show create table student; ....... ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 #也可以创建表时指定auto_increment的初始值，注意初始值的设置为表选项，应该放到括号外 create table student( id int primary key auto_increment, name varchar(20), sex enum('male','female') default 'male' )auto_increment=3; #设置步长 sqlserver：自增步长 基于表级别 create table t1（ id int。。。 ）engine=innodb,auto_increment=2 步长=2 default charset=utf8 mysql自增的步长： show session variables like 'auto_inc%'; #基于会话级别 set session auth_increment_increment=2 #修改会话级别的步长 #基于全局级别的 set global auth_increment_increment=2 #修改全局级别的步长（所有会话都生效） #！！！注意了注意了注意了！！！ If the value of auto_increment_offset is greater than that of auto_increment_increment, the value of auto_increment_offset is ignored. 翻译：如果auto_increment_offset的值大于auto_increment_increment的值，则auto_increment_offset的值会被忽略 比如：设置auto_increment_offset=3，auto_increment_increment=2 mysql> set global auto_increment_increment=5; Query OK, 0 rows affected (0.00 sec) mysql> set global auto_increment_offset=3; Query OK, 0 rows affected (0.00 sec) mysql> show variables like 'auto_incre%'; #需要退出重新登录 +--------------------------+-------+ | Variable_name | Value | +--------------------------+-------+ | auto_increment_increment | 1 | | auto_increment_offset | 1 | +--------------------------+-------+ create table student( id int primary key auto_increment, name varchar(20), sex enum('male','female') default 'male' ); mysql> insert into student(name) values('egon1'),('egon2'),('egon3'); mysql> select * from student; +----+-------+------+ | id | name | sex | +----+-------+------+ | 3 | egon1 | male | | 8 | egon2 | male | | 13 | egon3 | male | +----+-------+------+ 步长increment与起始偏移量offset:auto_increment_increment,auto_increment_offset
7.foreign key
一张表可以重复利用另一张表的字段，通过找出它们之间的关系，将它们关联起来，这就需要foreign key来实现
#表类型必须是innodb存储引擎，且被关联的字段，即references指定的另外一个表的字段，必须保证唯一 mysql> create table depart( -> id int primary key, -> name varchar(20) not null -> ); Query OK, 0 rows affected (2.03 sec) #dpt_id外键，关联父表（department主键id），同步更新，同步删除 mysql> create table employee( -> id int primary key, -> name varchar(20) not null, -> dpt_id int, -> foreign key(dpt_id) -> references depart(id) -> on delete cascade -> on update cascade -> ); Query OK, 0 rows affected (0.39 sec) #先往父表department中插入记录 mysql> insert into depart values -> (1,'欧德博爱技术有限事业部'), -> (2,'艾利克斯人力资源部'), -> (3,'销售部'); Query OK, 3 rows affected (0.06 sec) Records: 3 Duplicates: 0 Warnings: 0 #再往子表employee中插入记录 mysql> insert into employee values -> (1,'egon',1), -> (2,'alex1',2), -> (3,'alex2',2), -> (4,'alex3',2), -> (5,'李坦克',3), -> (6,'刘飞机',3), -> (7,'张火箭',3), -> (8,'林子弹',3), -> (9,'加特林',3) -> ; Query OK, 9 rows affected (0.07 sec) Records: 9 Duplicates: 0 Warnings: 0 #删父表department，子表employee中对应的记录跟着删 mysql> delete from depart where id=3; Query OK, 1 row affected (1.86 sec) mysql> select * from employee; +----+-------+--------+ | id | name | dpt_id | +----+-------+--------+ | 1 | egon | 1 | | 2 | alex1 | 2 | | 3 | alex2 | 2 | | 4 | alex3 | 2 | +----+-------+--------+ 4 rows in set (0.00 sec) #更新父表department，子表employee中对应的记录跟着改 mysql> update depart set id=22222 where id=2; Query OK, 1 row affected (1.83 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select * from employee; +----+-------+--------+ | id | name | dpt_id | +----+-------+--------+ | 1 | egon | 1 | | 2 | alex1 | 22222 | | 3 | alex2 | 22222 | | 4 | alex3 | 22222 | +----+-------+--------+ 4 rows in set (0.00 sec)
- 如何找出两张表之间的关系
分析步骤： #1、先站在左表的角度去找 是否左表的多条记录可以对应右表的一条记录，如果是，则证明左表的一个字段foreign key 右表一个字段（通常是id） #2、再站在右表的角度去找 是否右表的多条记录可以对应左表的一条记录，如果是，则证明右表的一个字段foreign key 左表一个字段（通常是id） #3、总结： #多对一： 如果只有步骤1成立，则是左表多对一右表 如果只有步骤2成立，则是右表多对一左表 #多对多 如果步骤1和2同时成立，则证明这两张表时一个双向的多对一，即多对多,需要定义一个这两张表的关系表来专门存放二者的关系 #一对一: 如果1和2都不成立，而是左表的一条记录唯一对应右表的一条记录，反之亦然。这种情况很简单，就是在左表foreign key右表的基础上，将左表的外键字段设置成unique即可
- 建立表之间的关系
#一对多或称为多对一 三张表：出版社，作者信息，书 一对多（或多对一）：一个出版社可以出版多本书 关联方式：foreign key
=====================多对一===================== create table press( id int primary key auto_increment, name varchar(20) ); create table book( id int primary key auto_increment, name varchar(20), press_id int not null, foreign key(press_id) references press(id) on delete cascade on update cascade ); insert into press(name) values ('北京工业地雷出版社'), ('人民音乐不好听出版社'), ('知识产权没有用出版社') ; insert into book(name,press_id) values ('九阳神功',1), ('九阴真经',2), ('九阴白骨爪',2), ('独孤九剑',3), ('降龙十巴掌',2), ('葵花宝典',3) ;
#多对多 三张表：出版社，作者信息，书 多对多：一个作者可以写多本书，一本书也可以有多个作者，双向的一对多，即多对多 关联方式：foreign key+一张新的表
=====================多对多===================== create table author( id int primary key auto_increment, name varchar(20) ); #这张表就存放作者表与书表的关系，即查询二者的关系查这表就可以了 create table author2book( id int not null unique auto_increment, author_id int not null, book_id int not null, constraint fk_author foreign key(author_id) references author(id) on delete cascade on update cascade, constraint fk_book foreign key(book_id) references book(id) on delete cascade on update cascade, primary key(author_id,book_id) ); #插入四个作者，id依次排开 insert into author(name) values('egon'),('alex'),('yuanhao'),('wpq'); #每个作者与自己的代表作如下 egon: 九阳神功 九阴真经 九阴白骨爪 独孤九剑 降龙十巴掌 葵花宝典 alex: 九阳神功 葵花宝典 yuanhao: 独孤九剑 降龙十巴掌 葵花宝典 wpq: 九阳神功 insert into author2book(author_id,book_id) values (1,1), (1,2), (1,3), (1,4), (1,5), (1,6), (2,1), (2,6), (3,4), (3,5), (3,6), (4,1) ;
单张表：用户表+相亲关系表，相当于：用户表+相亲关系表+用户表 多张表：用户表+用户与主机关系表+主机表 中间那一张存放关系的表，对外关联的字段可以联合唯一
#一对一 两张表：学生表和客户表 一对一：一个学生是一个客户，一个客户有可能变成一个学校，即一对一的关系 关联方式：foreign key+unique
#一定是student来foreign key表customer，这样就保证了： #1 学生一定是一个客户， #2 客户不一定是学生，但有可能成为一个学生 create table customer( id int primary key auto_increment, name varchar(20) not null ); create table student( id int primary key auto_increment, name varchar(20) not null, class_name varchar(20) not null default 'python自动化', level int default 1, customer_id int unique, #该字段一定要是唯一的 foreign key(customer_id) references customer(id) #外键的字段一定要保证unique on delete cascade on update cascade ); #增加客户 insert into customer(name) values ('李飞机'), ('王大炮'), ('守榴弹'), ('吴坦克'), ('赢火箭'), ('战地雷') ; #增加学生 insert into student(name,customer_id) values ('李飞机',1), ('王大炮',2) ;
- 练习：账号信息表，用户组，主机表，主机组
#用户表 create table user( id int not null unique auto_increment, username varchar(20) not null, password varchar(50) not null, primary key(username,password) ); insert into user(username,password) values ('root','123'), ('egon','456'), ('alex','alex3714') ; #用户组表 create table usergroup( id int primary key auto_increment, groupname varchar(20) not null unique ); insert into usergroup(groupname) values ('IT'), ('Sale'), ('Finance'), ('boss') ; #主机表 create table host( id int primary key auto_increment, ip char(15) not null unique default '127.0.0.1' ); insert into host(ip) values ('172.16.45.2'), ('172.16.31.10'), ('172.16.45.3'), ('172.16.31.11'), ('172.10.45.3'), ('172.10.45.4'), ('172.10.45.5'), ('192.168.1.20'), ('192.168.1.21'), ('192.168.1.22'), ('192.168.2.23'), ('192.168.2.223'), ('192.168.2.24'), ('192.168.3.22'), ('192.168.3.23'), ('192.168.3.24') ; #业务线表 create table business( id int primary key auto_increment, business varchar(20) not null unique ); insert into business(business) values ('轻松贷'), ('随便花'), ('大富翁'), ('穷一生') ; #建关系：user与usergroup create table user2usergroup( id int not null unique auto_increment, user_id int not null, group_id int not null, primary key(user_id,group_id), foreign key(user_id) references user(id), foreign key(group_id) references usergroup(id) ); insert into user2usergroup(user_id,group_id) values (1,1), (1,2), (1,3), (1,4), (2,3), (2,4), (3,4) ; #建关系：host与business create table host2business( id int not null unique auto_increment, host_id int not null, business_id int not null, primary key(host_id,business_id), foreign key(host_id) references host(id), foreign key(business_id) references business(id) ); insert into host2business(host_id,business_id) values (1,1), (1,2), (1,3), (2,2), (2,3), (3,4) ; #建关系：user与host create table user2host( id int not null unique auto_increment, user_id int not null, host_id int not null, primary key(user_id,host_id), foreign key(user_id) references user(id), foreign key(host_id) references host(id) ); insert into user2host(user_id,host_id) values (1,1), (1,2), (1,3), (1,4), (1,5), (1,6), (1,7), (1,8), (1,9), (1,10), (1,11), (1,12), (1,13), (1,14), (1,15), (1,16), (2,2), (2,3), (2,4), (2,5), (3,10), (3,11), (3,12) ;
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